Mounting structure of piezoelectric transformer and method of mounting piezoelectric transformer

ABSTRACT

In a structure in which a piezoelectric transformer element ( 11 ) is mounted on a circuit board ( 27 ) equipped with a circuit component for driving the piezoelectric transformer element ( 11 ), at least one of a fixing member ( 33, 35 ) and a supporting member ( 37, 39, 41 ) made of an elastic material having flexibility is interposed between the piezoelectric transformer element ( 11 ) and the circuit board ( 27 ) so as to cover vibration node portions ( 29, 31 ) of the piezoelectric transformer element ( 11 ) and at least a part of the remaining portion except the vibration node portions ( 29, 31 ). Thus, the piezoelectric transformer element ( 11 ) is fixed to the circuit board ( 27 ).

TECHNICAL FIELD

This invention relates to a structure in which a piezoelectrictransformer element for use in a piezoelectric inverter of a backlightfor a liquid crystal display or the like is mounted on a circuit boardequipped with circuit components and a method of mounting the same.

BACKGROUND ART

As a conventional mounting method of a piezoelectric transformerelement, there is known a mounting method in which the piezoelectrictransformer element is contained in a case and an external terminal ofthe case is connected by soldering or the like to a circuit boardequipped with a circuit component. Another mounting method is also knownin which no casing is carried out to avoid a problem of heat generationfollowing an increase in output power but a vibration node is fixed bythe use of a flexible elastic material, for example, silicone.

In order to adjust the brightness of a backlight, it is required tocarry out control of an inverter electrically connected to thebacklight. As a circuit system for such brightness adjustment, a burstadjustment is generally used.

This results in a problem of generation of an audible sound, which hasnot been caused in the conventional method of fixedly supporting thepiezoelectric transformer used in the inverter. The reason is asfollows. The piezoelectric transformer is generally driven in a singlemode. However, by addition of a brightness adjusting function, thepiezoelectric transformer itself is driven in a mode other than thesingle mode. Even if the piezoelectric transformer is fixedly supportedat a nodal point in the single mode, a nodal point in the other modewill be deviated from the supporting point. This results in generationof the audible sound in a mounted state.

Therefore, it is a first object of this invention to provide a mountingstructure of a piezoelectric transformer element, which can minimizegeneration of an audible sound even if it is used in vibration modes ofdifferent frequencies.

It is a second object of this invention to provide a method of mountingthe above-mentioned piezoelectric transformer element.

DISCLOSURE OF THE INVENTION

According to this invention, there is provided a mounting structure of apiezoelectric transformer element which is mounted on a circuit boardequipped with at least one circuit component for driving thepiezoelectric transformer element, wherein the piezoelectric transformerelement is fixed to the circuit board by the use of at least one of afixing member and a supporting member made of an elastic material havingflexibility and interposed between the piezoelectric transformer elementand the circuit board so as to cover vibration node portions of thepiezoelectric transformer element and at least a part of a remainingportion except the vibration node portions.

According to this invention, there is also provided a mounting structureof a piezoelectric transformer element which is mounted on a circuitboard equipped with at least one circuit component for driving thepiezoelectric transformer element, wherein the circuit board is formedin a manner such that an area between portions corresponding tovibration node portions of the piezoelectric transformer element andouter areas outside of the above-mentioned portions are depressedcomparing with the portions corresponding to the vibration node portionsand that the length across the outer areas exceeds the length of thepiezoelectric transformer element, the piezoelectric transformer elementbeing fixed to the circuit board by the use of a fixing member made ofan elastic material having flexibility and interposed between thepiezoelectric transformer element and the circuit board at the vibrationnode portions of the piezoelectric transformer element.

According to this invention, there is also provided a mounting method ofa piezoelectric transformer element which is mounted on a circuit boardequipped with at least one circuit component for driving thepiezoelectric transformer element, wherein the piezoelectric transformerelement is fixed to the circuit board by the use of at least one of afixing member and a supporting member made of an elastic material havingflexibility and interposed between the piezoelectric transformer elementand the circuit board so as to cover vibration node portions of thepiezoelectric transformer element and at least a part of a remainingportion except the vibration node portions.

According to this invention, there is also provided a mounting method ofa piezoelectric transformer element which is mounted on a circuit boardequipped with at least one circuit component for driving thepiezoelectric transformer element, wherein the circuit board is formedin a manner such that an area between portions corresponding tovibration node portions of the piezoelectric transformer element andouter areas outside of the above-mentioned portions are depressedcomparing with the portions corresponding to the vibration node portionsand that the length across the outer areas exceeds the length of thepiezoelectric transformer element, the piezoelectric transformer elementbeing fixed to the circuit board by the use of a fixing member made ofan elastic material having flexibility and interposed between thepiezoelectric transformer element and the circuit board at the vibrationnode portions of the piezoelectric transformer element.

Thus, in this invention, as a method of mounting a piezoelectrictransformer element on a circuit board equipped with at least onecircuit component for driving the piezoelectric transformer element, thepiezoelectric transformer element is fixed at vibration nodes by the useof a flexible elastic material (preferably, silicone or the like).Furthermore, another flexible elastic material is inserted in a portionother than the vibration nodes in a spot-like fashion or in parallel tothe vibration nodes to be used as a spacer. In this manner, thepiezoelectric transformer has a structure hard to transmit the vibrationto the circuit board upon excitation which is not a single modeexcitation. Thus, it is possible to suppress a heat generation and anaudible sound.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1(a) is a plan view showing a conventional mounting structure of apiezoelectric transformer element;

FIG. 1(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in FIG. 1(a);

FIG. 2(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to a first embodiment of this invention;

FIG. 2(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in FIG. 2(a);

FIG. 3(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to a second embodiment of this invention;

FIG. 3(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in (a);

FIG. 4(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to a third embodiment of this invention;

FIG. 4(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in FIG. 4(a);

FIG. 5(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to a fourth embodiment of this invention;

FIG. 5(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in FIG. 5(a);

FIG. 6(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to a fifth embodiment of this invention;

FIG. 6(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in (a);

FIG. 7(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to a sixth embodiment of this invention;

FIG. 7(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in (a);

FIG. 8(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to a seventh embodiment of this invention;

FIG. 8(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in (a);

FIG. 9(a) is a plan view showing a mounting structure of a piezoelectrictransformer element according to an eighth embodiment of this invention;and

FIG. 9(b) is a side view showing the mounting structure of thepiezoelectric transformer element illustrated in (a).

BEST MODE FOR EMBODYING THE INVENTION

Before describing the best mode for embodying this invention,description will at first be made about a conventional mountingstructure of a piezoelectric transformer element with reference to FIG.1 in order to facilitate an understanding of this invention.

Referring to FIG. 1(a) and FIG. 1(b), a piezoelectric transformerelement 11 comprises a rectangular piezoelectric ceramic plate or amultilayer structure (hereinafter referred to as a rectangularpiezoelectric plate 13) including internal electrode layers andpiezoelectric-ceramic layers, outer electrodes 15 and 17 formed on bothof the upper and the lower surfaces of the rectangular piezoelectricplate 13 to extend over an approximate half at the side of one end asdepicted by hatching, and an outer electrode 19 formed on an end surfaceof the rectangular piezoelectric plate 13 in the remaining approximatehalf not provided with the outer electrodes 15 and 17 as similarlydepicted by hatching. The outer electrodes 15, 17, and 19 are connectedto lead wires 21, 23, and 25 by soldering or the like, respectively. Inorder to mount the piezoelectric transformer element 11 on a circuitboard 27, they are bonded through fixing members 33 and 35 made of aflexible elastic material (a silicone-based adhesive or the like) andarranged on the lower surface of the piezoelectric transformer element11 beneath vibration nodes 29 and 31 thereof. One of the lead wires 21and 23 connected to the outer electrodes 15 and 17 is used as an inputterminal while the lead wire 25 connected to the outer electrode 19 isused as an output terminal. The other of the lead wires 21 and 23connected to the outer electrodes 15 and 17 is used as a commonterminal. When the input side is applied with an AC voltage having afrequency equal to a resonance frequency, the piezoelectric transformerelement 11 resonates. By this resonance, an AC voltage raised by astep-up ratio of the piezoelectric transformer element is producedbetween the input terminal and the common terminal.

Now, description will be made about embodiments of this invention withreference to FIG. 2 through FIG. 8.

Referring to FIG. 2(a) and FIG. 2(b), a piezoelectric transformerelement 11 according to a first embodiment of this invention has astructure similar to that of the conventional one illustrated in FIG. 1.Specifically, the piezoelectric transformer element 11 comprises arectangular piezoelectric plate 13, outer electrodes 15 and 17 formed onboth of the upper and the lower surfaces of the rectangularpiezoelectric plate 13 to extend over an approximate half at the side ofone end, and an outer electrode 19 formed on an end surface of therectangular piezoelectric plate 13 in the remaining approximate half notprovided with the outer electrodes 15 and 17. Like in FIG. 1, lead wires21, 23, and 25 are provided although not illustrated in FIG. 2(a) andFIG. 2(b).

In the first embodiment of this invention, the piezoelectric transformerelement 11 is mounted on a circuit board 27 via fixing members 33 and 35made of a flexible elastic material (a silicone-based adhesive or thelike) and introduced at and adhered to the lower surface of thepiezoelectric transformer element 11 beneath vibration nodes 29 and 31thereof.

Furthermore, in the first embodiment of this invention, disk-shapedspacer members 37 and 39 made of completely dry silicone such assilicone rubber as a flexible elastic material are introduced under anedge portion at one end of the piezoelectric transformer element 11 andadhered by the silicone-based adhesive. In addition, a disk-shapedspacer member 41 made of silicone as a flexible elastic material is alsointroduced under, and adhered by the silicone-based adhesive to, an edgeportion at the other end.

Thus, the piezoelectric transformer element is supported by the threespacer members 37, 39, and 41.

Referring to FIG. 3(a) and FIG. 3(b), a mounting structure of apiezoelectric transformer element according to a second embodiment ofthis invention is different from the structure illustrated in FIG. 2 inthat spacer members 41 and 43 also made of silicone as a flexibleelastic material are introduced under, and adhered by silicone-basedadhesive to, an edge portion at the other end of the piezoelectrictransformer element 11, thus the piezoelectric transformer element beingsupported by four points in total including those at the one end. Exceptthe above-mentioned difference, the structure is similar to that of thefirst embodiment illustrated in FIG. 2.

Referring to FIG. 4(a) and FIG. 4(b), in a mounting structure of apiezoelectric transformer element 11 according to a third embodiment ofthis invention, the piezoelectric transformer element 11 is similar instructure to each of the conventional one illustrated in FIG. 1 and thefirst and the second embodiments illustrated in FIG. 2 and FIG. 3.

As shown in FIG. 4(a) and FIG. 4(b), strip-like fixing members 33 and 35made of an elastic material having flexibility are arranged on the lowersurface of the piezoelectric transformer element 11 beneath vibrationnodes 29 and 31 thereof. Spacer members 45 and 47 each of which servesas a single strip-like supporting member are inserted and adhered at theinput side and the output side in parallel to the fixing members 33 and52 at the vibration nodes.

Referring to FIG. 5(a) and FIG. 5(b), in a mounting structure of apiezoelectric transformer element 11 according to a fourth embodiment ofthis invention, the piezoelectric transformer element 11 is similar in astructure to each of the conventional one illustrated in FIG. 1 and thefirst through the third embodiments illustrated in FIG. 1 through FIG.4.

As shown in FIG. 5(a) and FIG. 5(b), strip-like fixing members 33 and 35made of an elastic material having flexibility are arranged on the lowersurface beneath vibration nodes 29 and 31. Spacer members 45 and 47 eachof which is a single strip-like member are introduced under, and adheredto, the input side and the output side and extend in parallel to thefixing members 33 and 35 at the vibration nodes. The fourth embodimentis different from the embodiment illustrated in FIG. 4 in that astrip-like spacer 49 similar to the spacer members 45 and 47 isintroduced under, and adhered at, the center of the piezoelectrictransformer element 11 in parallel to the fixing members 33 and 35 atthe vibration nodes.

As specific examples according to the first through the fourthembodiments described above, piezoelectric transformer elements having athree-dimensional size of 53/83/3.3 mm were mounted on boards.Thereafter, comparison of characteristics was carried out between thefirst embodiment of this invention and the third embodiment of thisinvention as shown in the following Table 1.

TABLE 1 Products of Present Invention Conventional First Second ItemProduct Embodiment Embodiment Step-up Ratio 90 91 90 DrivingFrequency(kHz) 64.5 64.5 64.5 Heat Generation (° C.) 18 17 18 AudibleSound (dB) 70 61 62

As shown in the above Table 1, no substantial change and no substantialdeterioration were observed in heat generation, step-up ratio, anddriving frequency of the piezoelectric transformer, as compared with theconventional mounting method. In addition, the level of the audiblesound was reduced by 8 dB or more, as compared with the conventionalproduct. Thus, the characteristics of a practically acceptable levelwere obtained.

Referring to FIG. 6(a) and FIG. 6(b), in a mounting structure of apiezoelectric transformer element according to a fifth embodiment ofthis invention, the piezoelectric transformer element 11 has a structuresimilar to that of the conventional one illustrated in FIG. 1.Specifically, the piezoelectric transformer element 11 comprises arectangular piezoelectric plate 13, outer electrodes 15 and 17 formed onboth of the upper and the lower surfaces of the rectangularpiezoelectric plate 13 to extend over an approximate half at the side ofone end, and an outer electrode 19 formed on an end surface of therectangular piezoelectric plate 13 in the remaining approximate halfhaving none of the outer electrodes 15 and 17. In addition, the outerelectrodes 15, 17, and 19 are connected by soldering to lead wires 21,23, and 25, respectively.

In the fifth embodiment of this invention, the piezoelectric transformerelement 11 is mounted on a circuit board 27 by a fixing member 51 madeof a flexible elastic material (silicone or the like) introduced under,and adhered to, the entire surface of the piezoelectric transformerelement 11 including the positions beneath vibration nodes 27 and 29.

The above-mentioned fifth embodiment of this invention can provide theeffect similar to that of the mounting structure in each of the firstthrough the fourth embodiments.

Referring to FIG. 7(a) and FIG. 7(b), in a mounting structure of apiezoelectric transformer element according to a sixth embodiment ofthis invention, the piezoelectric transformer element 11 is similar instructure to those illustrated in FIG. 1 through FIG. 6. Specifically,the piezoelectric transformer element 11 comprises a rectangularpiezoelectric plate 13, outer electrodes 15 and 17 formed on both of theupper and the lower surfaces of the rectangular piezoelectric plate 13to extend over an approximate half at the side of one end, and an outerelectrode 19 formed on an end surface of the rectangular piezoelectricplate 13 in the remaining approximate half having none of the outerelectrodes 15 and 17. In addition, the outer electrodes 15, 17, and 19are connected by soldering to the lead wires 21, 23, and 25,respectively.

The sixth embodiment of this invention is different in structure fromthat illustrated in FIG. 6 in that the piezoelectric transformer element11 is mounted on a circuit board 27 via a spacer member 53 made ofsilicone as a flexible elastic material and serving as a supportingmember, which is introduced under the entire surface of thepiezoelectric transformer element 11 including the positions beneath thevibration nodes 18 and 19 thereof, and adhered thereto by asilicone-based adhesive.

The sixth embodiment of this invention can also provide the effectsimilar to those in the first through the fifth embodiments.

Referring to FIG. 8(a) and FIG. 8(b), in a mounting structure of apiezoelectric transformer element according to a seventh embodiment ofthis invention, the piezoelectric transformer element 11 has a structuresimilar to that of the conventional one illustrated in FIG. 1.Specifically, the piezoelectric transformer element 11 comprises arectangular piezoelectric ceramic plate or a multilayer structure(hereinafter referred to as a rectangular piezoelectric plate 13)including internal electrode layers and piezoelectric ceramic layers,outer electrodes 15 and 17 formed on both of the upper and the lowersurfaces of the rectangular piezoelectric plate 13 to extend over anapproximate half at the side of one end, and an outer electrode 19formed on an end surface of the remaining approximate half having noneof the outer electrodes 15 and 17. The outer electrodes 15, 17, and 19are connected by soldering to lead wires 21, 23, and 25, respectively.

In addition, a circuit board 27 is provided with a groove 57 formedbetween base portions 55 and 55 corresponding to vibration nodes 29 and31 of the piezoelectric transformer element 11, and grooves 59 and 59formed outside of the base portions 55 to extend over the width beyondthe ends of the piezoelectric transformer element 11.

In the seventh embodiment of this invention, the piezoelectrictransformer element 11 is mounted on the circuit board 27 in a mannersuch that the lower surface of the piezoelectric transformer element 11is adhered to the base portions of the circuit board 27 at the positionsbeneath the vibration nodes 29 and 31 via fixing members 33 and 35 madeof a flexible elastic material (silicone or the like).

The above-mentioned seventh embodiment of this invention can alsoprovide the effect similar to those in the first through the fourthembodiments. In addition, it is possible to prevent the contact betweenthe ends of the piezoelectric transformer element 11 and the circuitboard 27 due to warping of the circuit board 27 resulting from thedeviation in resonance frequency of the piezoelectric transformerelement 11. Therefore, generation of the audible sound can be reduced.

Referring to FIG. 9(a) and FIG. 9(b), in a mounting structure of apiezoelectric transformer element according to an eighth embodiment ofthis invention, it is mounted on a circuit board 73 equipped withcomponents for driving the piezoelectric transformer element 71 in apower supply circuit.

The above-mentioned piezoelectric transformer element is driven invibration modes of (1/2)λ or λ and comprises outer electrodes 75, 77,79, and 81 formed on both of the front and the back side surfaces of thetransformer. The piezoelectric transformer 71 is mounted on the circuitboard 73 via fixing members 87 and 89 made of a flexible elasticmaterial and interposed therebetween at the positions beneath vibrationnodes 83 and 85 of the piezoelectric transformer as well as supportingmembers 91, 93, and 95 similar to the spacer members in the firstembodiment to prevent generation of the sound. Thus, the mountingstructure of the eighth embodiment shows that the mounting structures ofthe first through the seventh embodiments can be applied to apiezoelectric transformer element having a different structure.

In the eighth embodiment of this invention, the fixing members 87 and 89are disposed at the portions of the vibration nodes (nodal points) 83and 85. However, if the fixing members 87 and 89 are disposed atpositions nearer to the both ends than the nodal points 83 and 85 and atpositions spaced by 5/1 of the whole length from the both ends or nearerthereto, the supporting members 91, 93, and 95 can be omitted.Furthermore, the fixing members 87 and 89 can be replaced by supportingmembers, further may be unnecessary to fix by adhesion or support thenodal points 83 and 85.

As described above, according to this invention, in the structure inwhich the piezoelectric transformer element for use in the piezoelectricinverter is mounted on the circuit board equipped with the circuitcomponents for driving the piezoelectric transformer element, use ismade of the mounting method in which the flexible elastic material isintroduced under, and adhered as the spacer to, the position except thevibration nodes. In this manner, it is possible to reduce generation ofthe audible sound without changing the characteristics such as the heatgeneration, the step-up ratio, and the driving frequency.

In addition, according to this invention, it is possible to provide themounting method for obtaining the mounting structure similar to thatdescribed above.

INDUSTEIAL APPLICABILITY

As described above, the mounting structure and the mounting method of apiezoelectric transformer according to this invention is adapted to theuse of the piezoelectric transformer element as a piezoelectric inverterof a backlight of a liquid crystal display or the like by mounting it ona circuit board equipped with a circuit component.

What is claimed is:
 1. A mounting structure of a piezoelectrictransformer element which is mounted on a circuit board equipped with atleast one circuit component for driving said piezoelectric transformerelement, wherein said circuit board is formed in a manner such that anarea between portions corresponding to vibration node portions of saidpiezoelectric transformer element and outer areas outside of theabove-mentioned portions are depressed comparing with the portionscorresponding to said vibration node portions and that the length acrosssaid outer areas exceeds the length of said piezoelectric transformerelement, said piezoelectric transformer element being fixed to saidcircuit board by the use of a fixing member made of an elastic materialhaving flexibility and interposed between said piezoelectric transformerelement and said circuit board at said vibration node portions of saidpiezoelectric transformer element.